You haven't really provided much information for me to advise you. It all depends on what you mean by cheap as your age, driving history, years licence held and budget are unknown. You could get a cheap Ford Focus for £800 and pay more in car insurance if you are a young driver etc but as for insurance goes I'm sure you have heard of short term car insurance. It might be worth it as you can have a flexible contract if you are unsure when your car will be ready. As for a cheap car there are loads but it all depends on how much you want to spend, you can get really old cars such as the old Nissan Micra for under £500 but remember that it has no power steering but it is economical and the reliability factor is very good. You could even get an old Toyota they are also very reliable but then again it depends on your budget. You could speak to a mechanic as he would be able to advise you on the best 'old' car to get for temporary use.
